1. Field of the Invention
The present invention relates to a multilayer coil component having the structure in which a magnetic ceramic element includes a spiral coil therein, the magnetic ceramic element being formed by firing a ceramic laminate in which coil-forming internal conductors primarily composed of Ag and magnetic ceramic layers are laminated to each other.
2. Description of the Related Art
In recent years, electronic components have been increasingly required to be miniaturized, and also as for coil components, a multilayer type has been becoming a mainstream.
Incidentally, in a multilayer coil component obtained by simultaneous firing of a magnetic ceramic and internal conductors, an internal stress generated by the difference in coefficient of thermal expansion between magnetic ceramic layers and internal conductor layers degrades magnetic characteristics of the magnetic ceramic and causes a problem in that the impedance value of the multilayer coil component decreases and/or fluctuates.
Accordingly, in order to solve the above problem, a multilayer impedance element has been proposed in which voids are formed between magnetic ceramic layers and internal conductor layers by a treatment to immerse a fired magnetic ceramic element in an acidic plating solution so as to avoid the influence of stress by the internal conductor layers to the magnetic ceramic layers and to overcome the decrease and/or fluctuation of the impedance value, as disclosed in Japanese Unexamined Patent Application Publication No. 2004-22798.
However, in the multilayer impedance element disclosed in Japanese Unexamined Patent Application Publication No. 2004-22798, since discontinuous voids are formed between the magnetic ceramic layers and the internal conductor layers by immersing the magnetic ceramic element in the plating solution so as to enable the plating solution to permeate the inside of the magnetic ceramic element through portions of the internal conductor layers which are exposed on the surfaces of the magnetic ceramic element, the internal conductor layers and the voids are formed between the magnetic ceramic layers, and the internal conductor layers are thinned, so that in practice, the ratio of the internal conductor layers present between the ceramic layers inevitably decreases.
Hence, a problem may arise in that a product having a low direct current resistance is difficult to obtain. In particular, in the case of a compact product, such as a product having dimensions of 1.0 mm, 0.5 mm, and 0.5 mm or a product having dimensions of 0.6 mm, 0.3 mm, and 0.3 mm, the thickness of each magnetic ceramic layer must be decreased, and internal conductor layers each having a large thickness are difficult to form while the internal conductor layers and the voids are both provided between the magnetic ceramic layers. Accordingly, the direct current resistance is not only decreased but also fracture of the internal conductors caused by the surge or the like is liable to occur, and as a result, a problem in that sufficient reliability cannot be ensured may occur.